linux-kernel - Re: [PATCH v3 2/2] x86, mwaitt: introduce mwaix delay with a configurable timer

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Message-ID: <CALCETrW6ZOTE7JcTQsNhJex5eaVQ8+z7MVGG-pfCOj=e47o10w@mail.gmail.com>
Date:	Thu, 11 Jun 2015 10:34:15 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Huang Rui <ray.huang@....com>
Cc:	Borislav Petkov <bp@...e.de>, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Fengguang Wu <fengguang.wu@...el.com>,
	Aaron Lu <aaron.lu@...el.com>,
	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	Tony Li <tony.li@....com>, Ken Xue <ken.xue@....com>
Subject: Re: [PATCH v3 2/2] x86, mwaitt: introduce mwaix delay with a
 configurable timer

On Thu, Jun 11, 2015 at 7:14 AM, Huang Rui <ray.huang@....com> wrote:
> MWAITX can enable a timer and a corresponding timer value specified in SW
> P0 clocks. The SW P0 frequency is the same with TSC. The timer provides an
> upper bound on how long the instruction waits before exiting.
>
> The implementation of delay function in kernel can lerverage the timer of
> MWAITX. This patch provides a new method (delay_mwaitx) to measure delay
> time.
>
> Suggested-by: Andy Lutomirski <luto@...capital.net>
> Suggested-by: Borislav Petkov <bp@...e.de>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Huang Rui <ray.huang@....com>
> ---
>  arch/x86/include/asm/mwait.h | 11 +++++++++++
>  arch/x86/lib/delay.c         | 41 ++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 51 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
> index ece8048..9b41580 100644
> --- a/arch/x86/include/asm/mwait.h
> +++ b/arch/x86/include/asm/mwait.h
> @@ -14,6 +14,8 @@
>  #define CPUID5_ECX_INTERRUPT_BREAK     0x2
>
>  #define MWAIT_ECX_INTERRUPT_BREAK      0x1
> +#define MWAITX_ECX_TIMER_ENABLE                BIT(1)
> +#define MWAITX_MAX_LOOPS               ((u32)-1)
>
>  static inline void __monitor(const void *eax, unsigned long ecx,
>                              unsigned long edx)
> @@ -80,4 +82,13 @@ static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
>         current_clr_polling();
>  }
>
> +static inline void mwaitx(unsigned long eax, unsigned long loops,
> +                         bool enable)
> +{
> +       if (enable)
> +               __mwaitx(eax, loops, MWAITX_ECX_TIMER_ENABLE);
> +       else
> +               __mwaitx(eax, 0, 0);
> +}

What's the purpose of the "enable" parameter?

--Andy
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